This invention relates to arc furnaces for steel production and the like, and more particularly to fluid cooled blocks for use in the roofs and walls of such furnaces.
Historically electric arc furnaces have been constructed of refractory bricks arranged to form a circular furnace with a refractory brick roof having holes for three graphite electrodes which are suspended above the furnace and lowered into it. An arc is maintained between the electrodes and a pool of molten metal or "melt" at the bottom of the furnace. Ore is charged into the furnace and a molten metal product is tapped from the melt.
The very high temperatures reached in the arc furnace, on the order of 1600.degree. C., result in heavy wear of the refractory brick and the destruction of the furnace in a relatively short time. In a typical electric arc steel furnace the average furnace roof and side walls made of conventional refractory brick survive for approximately 30 to 70 heats, or steel making melts, lasting some 10 to 14 days before they must be replaced. Replacement involves shutting down the furnace, permitting it to cool and then tearing down and replacing the damaged areas of sidewall and roof.
The vulnerability of the traditional refractory brick material to damage from the high temperatures generated inside the typical arc furnace has led to many efforts to either cool the refractory brick or replace it with material better able to withstand the high temperatures. Thus U.S. Pat. No. 4,091,228 describes an apparatus designed to cool the exterior walls of the furnace made of refractory brick, while U.S. Pat. No. 4,132,852 describes such an apparatus for cooling the refractory bricks in a furnace roof. In U.S. Pat. No. 4,152,534 there is taught a roof construction with fluid cooled channels spaced between the refractory bricks in a furnace roof. The attempted cooling of refractory bricks is not a satisfactory procedure however because the refractory materials are thermal insulators and channel little heat to the fluid cooling mechanism.
In U.S. Pat. No. 4,221,922 a somewhat different approach is taken with water cooled metal panels placed inside a conventional refractory brick furnace. According to the patent, a layer of slag forms on the metal surface to protect it from the furnace contents. The problems of maintaining and repairing or replacing such metal panels within the hostile environment of the hot furnace interior are obvious. U.S. Pat. No. 4,097,679 teaches a furnace wall with water cooled panels inside as well as outside.
A number of efforts have been made to substitute fluid cooled metal panels for all or part of the refractory bricks in the furnace walls and roof. Thus U.S. Pat. Nos. 4,122,295 and 4,161,620 each describe and claim water cooled metal wall panels to replace the refractory bricks, while U.S. Pat. Nos. 4,021,603 4,197,422 and 4,216,348 are concerned with water cooled metal roofs. Such metal panels are either welded, and thus susceptible to leaks, or cast iron or the like, with resultant heavy weight which is particularly undesirable in roof structures.
Yet another approach was tried in U.S. Pat. No. 3,990,686 where water carrying boxes were imbedded in a wall of carbonaceous material to cool it. Such a construction provides only limited cooling of the walls and has the further disadvantage that the entire furnace wall must be disassembled if a section wears and the water box must be replaced.